/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.orm.jpa.support;

import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.lang.Nullable;
import org.springframework.orm.jpa.EntityManagerFactoryAccessor;
import org.springframework.orm.jpa.EntityManagerFactoryInfo;
import org.springframework.orm.jpa.SharedEntityManagerCreator;
import org.springframework.util.Assert;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;

/**
 * {@link FactoryBean} that exposes a shared JPA {@link javax.persistence.EntityManager}
 * reference for a given EntityManagerFactory. Typically used for an EntityManagerFactory
 * created by {@link org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean},
 * as direct alternative to a JNDI lookup for a Java EE server's EntityManager reference.
 *
 * <p>The shared EntityManager will behave just like an EntityManager fetched from an
 * application server's JNDI environment, as defined by the JPA specification.
 * It will delegate all calls to the current transactional EntityManager, if any;
 * otherwise, it will fall back to a newly created EntityManager per operation.
 *
 * <p>Can be passed to DAOs that expect a shared EntityManager reference rather than an
 * EntityManagerFactory. Note that Spring's {@link org.springframework.orm.jpa.JpaTransactionManager}
 * always needs an EntityManagerFactory in order to create new transactional EntityManager instances.
 *
 * @author Juergen Hoeller
 * @see #setEntityManagerFactory
 * @see #setEntityManagerInterface
 * @see org.springframework.orm.jpa.LocalEntityManagerFactoryBean
 * @see org.springframework.orm.jpa.JpaTransactionManager
 * @since 2.0
 */
public class SharedEntityManagerBean extends EntityManagerFactoryAccessor
        implements FactoryBean<EntityManager>, InitializingBean {

    @Nullable
    private Class<? extends EntityManager> entityManagerInterface;

    private boolean synchronizedWithTransaction = true;

    @Nullable
    private EntityManager shared;


    /**
     * Specify the EntityManager interface to expose.
     * <p>Default is the EntityManager interface as defined by the
     * EntityManagerFactoryInfo, if available. Else, the standard
     * {@code javax.persistence.EntityManager} interface will be used.
     *
     * @see org.springframework.orm.jpa.EntityManagerFactoryInfo#getEntityManagerInterface()
     * @see javax.persistence.EntityManager
     */
    public void setEntityManagerInterface(Class<? extends EntityManager> entityManagerInterface) {
        Assert.notNull(entityManagerInterface, "'entityManagerInterface' must not be null");
        this.entityManagerInterface = entityManagerInterface;
    }

    /**
     * Set whether to automatically join ongoing transactions (according
     * to the JPA 2.1 SynchronizationType rules). Default is "true".
     */
    public void setSynchronizedWithTransaction(boolean synchronizedWithTransaction) {
        this.synchronizedWithTransaction = synchronizedWithTransaction;
    }


    @Override
    public final void afterPropertiesSet() {
        EntityManagerFactory emf = getEntityManagerFactory();
        if (emf == null) {
            throw new IllegalArgumentException("'entityManagerFactory' or 'persistenceUnitName' is required");
        }
        if (emf instanceof EntityManagerFactoryInfo) {
            EntityManagerFactoryInfo emfInfo = (EntityManagerFactoryInfo) emf;
            if (this.entityManagerInterface == null) {
                this.entityManagerInterface = emfInfo.getEntityManagerInterface();
                if (this.entityManagerInterface == null) {
                    this.entityManagerInterface = EntityManager.class;
                }
            }
        } else {
            if (this.entityManagerInterface == null) {
                this.entityManagerInterface = EntityManager.class;
            }
        }
        this.shared = SharedEntityManagerCreator.createSharedEntityManager(
                emf, getJpaPropertyMap(), this.synchronizedWithTransaction, this.entityManagerInterface);
    }


    @Override
    @Nullable
    public EntityManager getObject() {
        return this.shared;
    }

    @Override
    public Class<? extends EntityManager> getObjectType() {
        return (this.entityManagerInterface != null ? this.entityManagerInterface : EntityManager.class);
    }

    @Override
    public boolean isSingleton() {
        return true;
    }

}
